In a computer system, DMA (Direct Memory Access) is generally used in order to transfer data without loading the CPU. Data transfer by DMA is controlled by a DMA transfer control device and performed between memory and an input/output device. When there is a plurality of input/output devices and each of the input/output device requests data transfer, a plurality of DMA transfer control devices is provided. These data transfer paths are called “DMA channels.”
When there is a plurality of DMA channels, an arbiter arbitrates between the data transfer requests in order to utilize a system bus to which the memory and the plurality of input/output devices are connected in common. The round-robin method and fixed priority method are used for this arbitration (for instance, refer to Patent Document 1).
However, these arbitration methods are not suitable when one wants to dynamically control the data transfer rate. Meanwhile, there is a method that improves the efficiency of the DMA transfers by measuring the DMA transfer rate and dynamically controlling DMA transfers based on the DMA transfer rate (refer to Patent Document 2).
[Patent Document 1]
Japanese Patent No. JP3202272B
[Patent Document 2]
Japanese Patent Kokai Publication No. JP2005-4563A